1. Field of the Invention
The present invention is directed to an apparatus for extracorporeal lithotripsy which includes a shock wave source that can be selectively driven to generate high-intensity shock waves converging in a focus zone to disintegrate a calculus, and low-intensity shock waves for imaging purposes.
2. Description of Prior Art
In the disintegration of calculi using extracorporeal devices, the location of the calculus to be disintegrated, for example a kidney stone, is first identified in the body of the patient with a suitable locating system. The lithotripsy apparatus is then aligned relative to the body of the patient so that the calculus to be disintegrated is situated in a focus zone of the apparatus. Shock waves are then generated which converge in the focus zone, and which interact with the calculus to generate mechanical stresses which initially decompose the calculus into fragments and into fine grit, with the fragments being made progressively smaller as the treatment continues, until the calculus has completely disintegrated into particles which can be naturally eliminated (excreted).
German AS2722252 discloses an extracorporeal lithotripsy apparatus of the type using a bath of water in which the apparatus and the patient are disposed, the water serving as a propagation medium for the shock waves. In this system, a number of pressure sensors, spatially separated from each other, are provided which permit locating of a calculus to be disintegrated. The pressure sensors are connected to a reception circuit, and register the spherical waves emanating from the calculus after the calculus has been charged with a low-intensity shock wave. This registration is possible as a consequence of known diffraction phenomena. It is also necessary, however, to initially align the apparatus relative to the body of the patient before such a low-intensity shock wave is generated, and for this purpose this known system also includes an ultrasound sector applicator to permit alignment of the patient relative to the stationary shock wave generator so that the calculus is situated in the region of the focus zone of the shock waves. In addition to being used for imaging purposes, the low-intensity shock waves also serve as the means for disintegrating the calculus.
It is usually desirable, however, to obtain information as to the effectiveness of the treatment, i.e., the degree of disintegration of the calculus, during the course of the treatment to permit a determination to be made as to the extent that the calculus has decomposed into fragments or into grit, since the amount of further treatment will be determined on this basis. This is not possible in the system described in German AS2722252, because the ultrasound waves emitted by the ultrasound sector applicator cannot penetrate into a collection of fragments or grit due to their short wavelength. The ultrasound waves are instead reflected at the boundary surface of the collection which faces toward the ultrasound sector application. The individual fragments or grit can therefore not be resolved in an image using this known ultrasound system. It is also not possible to monitor the degree of disintegration using the echo signals of the low-intensity shock waves because the information obtained using the pressure sensors in this known apparatus is essentially identical to that obtained with an ultrasound applicator operated in an A-imaging mode.